Another difference file, for G.flac (amp_stx):
This also has a gain of 200. There is less hiss, but much more hum, the level of which depends on the signal. Some distortion can be heard as well.
Edit: the increased amount of hum is partly an artifact of the difference extraction. That is because the hum also shows up in the measured frequency response to a small extent, so the equalization is less accurate at that frequency and its harmonics. This effect is also responsible for the reverb-like sound that can be heard at some parts of the sample.
For the other files, where the DAC and ADC do not share the same clock, extracting a difference signal is more problematic, because with a long sample (more than 3 minutes), there is too much drift over time due to clock frequency variation.
Edited by stv014 - 3/3/13 at 11:18am